The Torygraph also prints Quentin's full - and lengthy - resignation attack on David Cameron in all its detail.
Well worth reading.
UPDATE: Gordon Brown has welcomed Quentin to Labour saying he's highly respected by all sides in Parliament.
Gordon Brown said:
Quentin Davies is a senior parliamentarian and he commands respect on all sides for his expertise and his dedication to public service, and I welcome him to the New Labour party.What a tremendous start to a new era for our country.
On Sunday, I said I was determined to reach out to those who share our values and who would like to be part of building a more just society.
I said we had to reach out to people who want to change from the old politics, who yearn for a public life founded on principles, who are inspired by what we as a nation can achieve together - and asked them to join us. I am delighted that Quentin Davies has done so today.
UPDATE 2: FT says it's a 'massive blow' to Cameron.